Frequency reuse is a conventional technique for increasing wireless system capacity while reducing inter-cell interference. FIG. 1 illustrates a conventional N=3 frequency reuse pattern where the distance separation between co-channel base stations is always maintained at 3R, where R is the radius of a cell.
Some commercial mobile radio service (CMRS) systems, such as the iDEN system owned and operated by Nextel Communications, Inc., of Reston Va., currently operate within the 800 and 900 MHz frequency bands, a frequency spectrum known as Specialized Mobile Radio (SMR). In the SMR frequency spectrum, channels are interleaved and ownership of channels may change in 25 kHz increments. Therefore, CMRS system operators who operate in the SMR frequency spectrum use 25 kHz channel spacing for frequency reuse cell planning. The 25 kHz channel spacing is due to FCC requirements for masking certain emissions outside of authorized channels. Accordingly, 25 kHz channel spacing is the only option for frequency planning for CMRS system operators who currently operate iDEN system within the SMR spectrum.
FIG. 2 illustrates an exemplary frequency channel. As illustrated in FIG. 2, the 25 kHz channel comprises four sub-carriers and two 3–4 kHz guard bands. The two guard bands allow for compliance with the FCC rule that CMRS system operators who operate within the SMR frequency spectrum provide a sufficient rejection at the channel edge to protect against interference to adjacent channel licensees.
The FCC has released a Report and Order on 800 MHz SMR realignment to improve public safety communications and mitigate the potential harmful interference to public safety. By this Report and Order, public safety systems will be relocated to a lower portion of the 800 MHz and SMR band, and CMRS system operators will occupy contiguous 7+7 MHz of spectrum in the upper portion of the band. The nationwide contiguous spectrum position could provide more flexibility in frequency planning.